Structural Reinforcement Design for Model Aircraft

ABSTRACT

This invention is of a reinforcement kit which is intended to supply structural elements, or supplement and add to any existing structural elements in Radio Controlled aircraft, especially those craft that are constructed of expanded or extruded plastic foam, for the purpose of limiting or eliminating structural damage to the airframe caused by crashing or by stresses from extreme aerobatic maneuvering. The intention is to greatly extend the life and enhance the value of the Radio Controlled craft by making it possible for it to withstand
         1) a greater number of impacts,   2) impacts having a greater force   3) a greater amount of stress, colloquially referred to as “G Forces”, exerted on the airframe during aerobatic maneuvering and impacts with other objects or surfaces, and   4) to limit or eliminate airframe damage caused by handling, securing, and transporting the craft

BRIEF DESCRIPTION OF THE INVENTION

The invention consists of a plurality of Rods made from a flexible plastic material in conjunction with reinforcing bands, plates and joining devices, also made of a plastic material. Individual parts of the invention are attached one another and to an RC Craft by means of adhesives, and are designed to create a flexible structural framework that works in conjunction with the expanded plastic foam material of the craft to create a multi-part structure with a level of strength that is greater than the combined strength of the individual component materials. The ultimate aim of the invention is to offer a high level of protection against damages caused by impact or from excessive motion related stress, commonly known as “G Forces” The invention can also be installed to good effect in craft built using the frame with skin construction method. It is the claim of the inventor that this invention is unique in the field of RC flying, and will greatly benefit those who adopt it's use.

This invention may seem a simple and obvious idea, but as of the date of this filing, no manufacturers of RC craft include a system like this invention in their products, nor does any entity other than the inventor offer a system like this invention to the public, even though the inventor has publicized the invention from soon after the allowable date.

The typical basic design of foam craft being marketed at the time of this application is such that the expanded or extruded foam parts of the craft act as both the structural and cosmetic portion of the craft. The parts are designed and manufactured as an outer shell with enough thickness to hold it's shape in flight, and with built up areas of the moulded form that act as structural members like bulkheads. This means that all of the structural strength of a typical RC airplane is derived from a material that has less strength than an equivalent thickness of paper. This invention provides for a framework with a large measurable difference in strength, and the invention can be retrofitted into most existing craft or included into the manufacturing process of new aircraft designs.

The general design of the invention addresses potential areas of damage known from physical testing of some 75 separate examples typical craft.

It is the claim of the inventor that this is a unique combination of parts that achieve the heretofore unachievable goal of reinforcing a craft against damages caused by accidental impact during normal reasonable use. Up to this point, an individual involved in this hobby could expect to destroy their craft in an accident, rendering them unable to continue their pursuit of happiness. The incidence of the destruction of implements, tools, craft, or machinery necessary to engage in some other recreational pastime is much lower than that associated with flying RC airplanes, and this invention brings the RC flying hobby to a par with others in this respect. Imagine requiring new bowling ball each time you got a gutterball during a game! That has been the lot of the RC pilot—until now.

DEFINITIONS, TERMS AND ELEMENTS

adhesives—various commercially available adhesives, including but not limited to hot glue, urethane glue, contact cement, Cryanoacrylate, epoxies, and “double sided” adhesive tapes.

Crash Damage—damage to the structure of the aircraft from impact with other aircraft or stationary objects, including but not limited to deformation, tearing or ripping, compression, or other breakage of the structure or shape that renders the aircraft un-useable

expanded plastic foam or foam—the material used in the construction of typical RC aircraft. Various types of plastic (polyethelene, polyolefin, polystyrene, and others) are made into expandable beads that are placed in moulds and heated, expanding in the moulds to form complex shapes, or extruded

Rods—Sructural members of various dimensional sizes and shapes, including but not limited to round or square profile solid rods or hollow tubes, and other various solid or hollow profile extruded or moulded shapes (examples would include rods with cross sectional shapes of the letters of the alphabet) The most common profile shapes are round or square, because of the lower cost of these shapes. These structural members are made from extruded or moulded plastic like materials such as High Density Polyethelene, Carbon Fiber and epoxy, nylon, vinyl, and other plastic like materials

reinforcing bands, plates and joining devices—These structural members are made from extruded or moulded plastic like materials such as High Density Polyethelene, Carbon Fiber and epoxy, nylon, vinyl, and other plastic like materials. Their purpose is to physically join the individual rods or other parts, and protect adjacent foam shapes by the process of joining the structural members together using adhesives. A typical joining device would be a moulded part with hollow sockets or sleeves that accept 2 or more other structural members, which are fastened to the joining device with adhesives

BACKGROUND OF THE INVENTION

The initial reason for the invention was that the inventor, like nearly all other inexperienced RC pilots, experienced numerous mishaps that resulted in the damage or complete destruction of the RC aircraft, ending the pursuit until the aircraft was repaired or replaced. The inventor wanted a craft that could withstand routine crashes and other stresses and keep flying. Imagine needing a new bowling ball or time consuming repair to the alley each time you got a gutterball! The aim was to radically change the face of the hobby of RC flying by bringing the incidence of “game-stopping” damage down, to be on a par with other sports and hobbies.

We found that there was, and still is, a great deal of resistance from RC pilots, although direct experience using and benefitting from the product removes the individual's resistance. The negative “mind-set” of many in the field regarding this topic have kept most experimentation with designs like this invention at a minimum, and it is therefore difficult to find much published information. A web search of our tradename for the invention, (“Crashproofing”) will result in many pages by or about our 2 companies, www.killerplanes.com and www.crashproofplanes.com, and not much else.

After diligent search performed by the inventor and associates, we have not been able to locate any products available on the market that specifically resemble this invention. Certain models are manufactured with one or more elements of this design, such as two “spars” in a wing, but there are no products available with this design installed in them, nor does anyone other than the inventor offer for sale or for free, systems resembling this invention. Additionally, we have not been able to locate any meaningful information pertaining to reinforcing foam RC Airplanes against crash damage other than information published by the inventor and his company (www.crashproofplanes.com). Our attempts to educate the people involved in this hobby about the benefits of reinforcing an RC airplane have been met with ridicule for a long time, but it is finally catching on, because it actually works.

PRIOR ART KNOWN TO THOSE SKILLED IN THE ART

http://www.killerplanes.com/crashproofplanes

PRIOR ART KNOWN TO THOSE SKILLED IN THE ART

Most of the strength of this design is derived from flexible plastic types of material such as extruded carbon fiber rods and tubes. This new material's strength to weight ratio now makes designs like this possible for the first time.

Tensile strength of carbon fiber and other materials:

http://en.wikipedia.org/wiki/Ultimate_tensile_strength

http://www.dragonplate.com/sections/technology.asp

http://www.christinedemerchant.com/carboncharacteristics.html

http://nida-core.com/spanish/fusiprod_sto.htm

DETAILED DESCRIPTION OF THE INVENTION

All illustrations of the drawings are for the purpose of describing selected versions of the present invention and are not intended to limit the scope of the present invention.

The present invention is a method and apparatus for a structural reinforcement design for model airplanes that can be retrofitted to existing planes or installed during manufacture. The Reinforcement kit comprises a plurality of plastic like rods and plates (such as Carbon fiber/epoxy resin, plastic, or nylon) which are retrofitted to an existing model airplane, glued onto or drilled into the parts, or glued onto (or molded into the foam parts of) a factory made airplane. Kits may be modified to suit specific airplane designs by changing the length and/or diameter and specific location of rods, and/or adding or subtracting rods. (i.e.—adding rods in the nose area or changing the reinforcement of the wing attachment). The present invention is for an addition to an industry-wide standard construction method, and can be modified to fit most plane designs.

The present invention comprises one or more retainer rings in the fuselage, a plurality of fuselage rods, a plurality of cross rods, a plurality of wing attachment rods, a plurality of wing rods and spars, and a plurality of stabilizer rods. The present invention can comprise a plurality of mechanical joints. The joint can be a pair of sleeves connected by a swiveling pin, to allow for varying intersection angles of rods, or a pre-moulded part with sockets. The rod is inserted in the joint or socket and glued in place.

FIGS. 6, 7, 8 and 9 show a typical after market installation of the preferred embodiment of the present invention in a craft consisting of a fuselage, main wing, and tail with a plurality of openings, a plurality of longitudinal and latitudinal fuselage reinforcing rods (typical rod location), and a plurality of wing and tail rods. The drawings are described further in BRIEF DESCRIPTION OF THE DRAWINGS, below

The figures show a typical manufactured installation of the preferred embodiment of the present invention in a fuselage that comprises a canopy opening, a built out area with rod glued in surface groove, a built out area with embedded rod, a plurality of wing openings, a plurality of cross rods glued on a bulkhead, an outer side (skin), a bulkhead (structural support), a wiring opening in the bulkhead, and a plurality of longitudinal reinforcing rods (typical rod location).

The present invention is meant to act as a “skeleton” for all of the major structural areas. Unlike the framework parts that are used to make traditional airplane structures, this “skeleton” is far simpler (it does not need to be shaped to hold the skin) and made of materials that are, relatively speaking, nearly unbreakable, and light enough to have a negligible effect on lift and performance. Therefore, it can be used to good effect on planes made of expanded or extruded plastic foam type of material, as well as planes made of “framework and skin” design.

The purpose of the kit is to reinforce all of the major airframe components of the airplane to minimize impact damage from crashing or stress damage from aerobatic maneuvering. Some plane designs contain one or two wing spars made of plastic like rods or bars, and a few contain other similar parts, (like tail boom rods, or a rod in the horizontal tail). The present invention is a design for an after-market kit that comes with instructions for installation in commercially available model planes. In essence, upon installation, the kit becomes the structural part of the plane, and the pre-existing plane (foam) materials do double duty as a shell and an impact absorbing connective material that joins and protects a new framework. The framework is designed to cross-connect all of the major airframe components with new structural parts, further adding to the strength by reinforcing all of the “joints” where wings and fins are attached by crossing the seams where they attach, and to reinforce the entire length, to the extent possible, of all airframe parts, from “tip to tip”, by using single rods or overlapping pieces of rods that extend the full length of the part (i.e. the fuselage or the wing)

The present invention comprises a plurality of components that reinforce all of the areas on a model airplane that has a higher incidence of damages, including compression, crushing, cracking, tearing, fracturing and structural dismemberment. Some good examples of spots on a typical model plane airframe that have a high incidence of damage and that are addressed by this design are; a nose, a plurality of wing attachments, and any part of the wing that has areas removed to accommodate control surfaces (like flaps) and mechanical parts (like servos, landing gear, etc). Unlike pilots in real planes, most model pilots fly with abandon, and the planes are subject to numerous collisions that planes with passengers would hopefully never encounter. This design allows a pilot to continue flying a plane that may otherwise have been destroyed in such encounters. Variations on plane design, such as rear mounted motors and hard shell nosecones, can make use of this structural design for historically unprecedented survivability of a plane.

The preferred embodiment of the present invention comprises a plurality of basic components as described here:

1—Fuselage rods that run the length of the fuselage. This can be as few as one larger diameter rod, but two or more smaller ones work better. Three smaller rods (as shown) are recommended for the triangular structural shape obtained. These longitudinal rods can also be constructed of larger diameter tubes with smaller rods or tubes inserted inside and extending past the front of the former, with a retainer to limit depression, forming a piston type shock absorber to absorb the energy of impacts. The retainer ring (2) can be attached to the ends of several rods with this feature incorporated. These rods are flexible, with the amount of curvature based on the composition of the rod (solid or hollow, wall thickness, diameter, etc) and can be curved to fit most of the contours of most plane designs. Another reason for multiple longitudinal rods is to ensure “coverage” throughout the complex curves of an airframe design.

2—Fuselage rod retainer rings. Simply described, a ring made of a plastic material that contacts the longitudinal rods, and is attached to them with glue. Many modern types of glue are strong enough to replace a traditional molded and fitted joint, and are employed here. (Glues like “hot glue” also retain their flexibility, making the joint even more dynamic) The ring can be various shapes and sizes to fit the specific plane model, and can be used as attachment points for other parts of the plane, such as motors, servos, etc. These are optional but recommended, and can be placed either just at the front, or at the front and several other points along the length of the fuselage. Attaching the rods together spreads out the force of an impact to an even greater area, and is recommended for higher resistance to impact damage, but not necessary.

3—Fuselage cross rods. Almost all foam airplane fuselages consist of 2 left and right halves that are glued together. These halves often separate on impact, and the cross rods hold them together, helping to maintain structural integrity.

4—Main center wing spar (if any). These connect the 2 wing halves into one more cohesive unit, and strengthen the wing root of any wing, whether the wing is made of halves or a continuous structure. An optional rod can be included in the retro fit kit to replace these with stronger ones. In a plane that is manufactured with this design incorporated, the wings have the additional rods described in #5.

5—Wing rods and spars. The existing wing spars in available plane design are the minimum necessary to maintain wing integrity while flying. The rods and spars in this design are additional rods to protect all of the weak areas of the wing from tip to tip against stress damages from impact and maneuvering—the wing areas of a plane are the highest stress areas during maneuvering, and repeated flexing during high-G maneuvers reduces the strength of the structural foam, creating weak points in the airframe through usage. This design includes rods to address this problem, as well as protect against impact damage.

6—Wing and fin attachment rods. These protect and reinforce the area of the wing that attaches to the fuselage, such as the holes for the screws that hold the wings on, and can also be joined together with a strap on planes that have left and right wing halves, to hold the halves together. These rods are also used on the fuselage at the attachment points (i.e. the nuts for the wing screws) to reinforce those. These rods work by spreading the stresses across a far greater area—during a crash, a wing can easily separate from the plane because the screws rip right through the small area they penetrate. When a rod that is attached to the wing-screw retainer (the “washer”) is bonded to the wing, a far greater force is needed to “traumatically” remove the wing.

7—Rods for the vertical and horizontal tails (stabilizers). These rods reinforce the entire length of the surface to the extent possible, and intersect and connect with the fuselage rods to provide solid structural support for the joints.

More rods may be added to this basic design, either to increase the strength of specific “trouble spots” like the nose, or to reinforce the remaining areas of the plane (the motor mount, wingtips, control surfaces, hatches or canopies, landing gear, etc)

The individual pieces that comprise this design can be molded or drilled into, or glued onto parts of an RC plane during manufacture, either in grooves cut for the purpose or directly onto a flat surface. The design of the other (i.e.: expanded plastic foam) components of the plane accommodate these structural members by providing built out areas to glue the straight rods onto, or drill or mold them into. The present invention can also be installed as an after-market kit on nearly all commercially available RC airplane designs.

This kit is designed to reinforce model aircraft with nearly any construction. The description of the kit and its installation are based on the two main methods of construction that is used in over 95% of the planes currently being offered on the market. Most of these planes are made of expanded plastic foam, molded to shapes with all of the airframe details (i.e.; contours, rivets and panel lines) molded on the outside, and structural members designed to reinforce the particular model's shape on the inside, like bulkheads and areas of the outer shell that have increased thickness for strength. The other method is a very light framework made of laminated softwood, covered with a “skin” of thin wood or plastic. Both of these methods have the same basic layout, which affords the modeler access to the interior of the fuselage at several points, such as canopy opening and wing openings, as shown in FIG. 4. For an after-market installation, it is a simple process to drill through Styrofoam or thin softwood bulkheads while observing location and progress of drill along the inside of the “skin” through fuselage openings, and then to insert the reinforcing rods and apply glue in the same manner.

Much like in a conventional aircraft, or a car, or even a house, the outer “skin” of the original aircraft design does double duty as a structural member with this kit. Newly developed glues, like epoxies and hot glues, act much like weld joints on steel, creating a joint that is sufficient to the needs of this application. Therefore, many of the structural members in the design are glued together wherever they come in contact. There are physical joints that are employed wherever possible, such as retaining rings or at intersections of rods. These joints, whether physical or glue, distribute the stress forces across a larger number of rods.

To accommodate for aftermarket installation of this “kit” in different plane designs, the rods and other members of this design are cut to specific sizes from “stock”, and supplied in “kit” form with written instructions describing placement and attachment, so the customer can install the kit at home with simple hand tools. (i.e.: “Rod A goes against surface B and is attached with hot glue”) There are no special tools or processes necessary to install this product other than regular “hand tools”, although a drill guide is helpful. A drill guide can be made by drilling a hole with the bit through a wood block, which can be attached to a brace which then holds the bit at a specific angle, allowing even an inexperienced modeler to drill the holes necessary for the installation.

Although the invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as herein described.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the right half of a typical RC aircraft fuselage made from 2 lateral halves using expanded foam construction, with a motor compartment (1), fuel and control compartment (2), and bulkheads (3) moulded into the shape for strength, with wing mounting nuts (4) attached to the fuselage, and the vertical tail (5) included as part of the right half of the moulded fuselage

FIG. 2 shows a typical fuselage comprised of 2 lateral halves, with the horizontal tail (6) and vertical tail (5) in place. A typical propeller with nosecone (7) is shown at left, detached from the fuselage. Shown also is a removable hatch cover (8), and the wing mounting nuts (4)

FIG. 3 shows a typical compete RC aircraft, comprised of the fuselage (9) with hatch cover (8) tail fins or wings (5) and (6), and main wings (10). The wings shown are comprised of 2 halves and attached to the fuselage by means of screws. Typically, the screws pass through mounting plates that are fastened to the wings (11), and fasten to nuts which are fastened to the fuselage. The tail sections may be attached with screws in the same manner, or fastened to the fuselage with adhesives. The center seam shown on the top of the fuselage (12) is consistent with the other views The propeller with nosecone (7) is shown in place on this drawing, to show typical placement. No landing gear is shown on any of the drawings for reasons of simplification. The aircraft shown in these drawings is a propeller driven aircraft with a typical high wing configuration. The invention is a modular design that can be modified to accommodate different shape wings mounted at different locations on the fuselage, or “flying wing” designs where the fuselage is incorporated into the shape of the wing, or ducted fan designs where the motive power is provided by a fan with motor enclosed in a shroud (the “duct”) and mounted in the fuselage with appropriate air intake and exhaust ductwork moulded into the fuselage halves, or located in a separate motor pod mounted on the wing or fuselage.

FIG. 4 and FIG. 5 show the 2 drawings that will be used for the purpose of showing parts of the invention in their relative locations. The first drawing is of a fuselage with no main wing (13), and the second is of a fuselage with the main wing in place (14). Drawings showing the invention do not include a propeller and nosecone, and are shown in light grey (dotted line) for ease of identification of the parts of the invention, which are shown in black (solid line). The parts of the invention are superimposed over these drawings to show general location, and rods and other parts of the invention are shown in black line. The various weights of the lines showing the parts of the invention in the drawings is not relative to scale, they are only to indicate parts that are thicker or thinner relative to one another, and to assist in the visual identification of different parts of the invention.

FIG. 6 shows the main fuselage rods (15) and retaining bands (16), and longitudinal wing nut reinforcing rods (17)

FIG. 7 shows typical cross fuselage rods (18), which are fastened to an interior bulkhead which is delineated with a broken line (19), latitudinal wing nut reinforcing rods (20), fuselage rear rod (21), vertical tail rod (22) and horizontal tail rod (23)

FIG. 8 shows the wing spars: the main center spar (24), the main outer spars (25), the front (26) and rear (27) wing root spars, and the front wingtip spars (28). Also shown are the rudder spar (29) and elevator tip spars (30), which are included in certain aircraft designs.

FIG. 9 shows 2 types of wing screw reinforcing rods: a single longitudinal rod reinforcing both front and rear screws (31), and dual latitudinal rods, each reinforcing one wing screw (32). Also shown are the optional nose reinforcing plates (33), which are fastened onto the inner or outer sides of the fuselage using adhesives 

1. This system of structural elements succeeds in producing it's intended result, which is to reduce or eliminate damage in RC aircraft and other craft from crashes, impacts, and aerobatic maneuvering.
 2. The combination of the elements as described herein work to produce a “super” structure with heretofore unmatched capabilities to withstand stresses that could conceivably destroy a similar model that did not include this invention in it's composition.
 3. This invention is able to be both installed in new construction and retrofitted into existing designs, and that no other systems shown in Prior Art are able to be both installed in new construction and retrofitted into existing designs in this manner.
 4. (canceled) 